Noise reduction systems for electrical transformers

ABSTRACT

A system for reducing noise generated in an electrical transformer due to changing of size and shape of the ferromagnetic core when excited with alternating electric current. The noise reduction system comprises attaching flexible fibers to parts of the ferromagnetic core and parts of the housing or casing of the transformer. The flexible fibers absorb energy from the air column set up by the core when it changes size and shape and reduces the effectiveness of the air column in setting up objectional audible noise.

United States Patent James L. Rotruck inventor Sharon, Pa.

Appl. No. 876,768

Filed Nov. 14, 1969 Patented May 18, 1971 Assignee Westinghouse Electric Corporation Pittsburgh, Pa.

NOISE REDUCTION SYSTEMS FOR ELECTRICAL TRANSFORMERS 8 Claims, 2 Drawing Figs.

Int. Cl H01f 15/00 Field of Search 336/100, 219

[56] References Cited UNITED STATES PATENTS 2,892,507 6/1959 Kirkpatrick 336/100X 3,077,946 2/ 1963 Wilkins 336/10OX 3,260,974 7/ 1966 Specht et al. 336/ lOOX Primary Examiner-Thomas .I. Kozma Attorneys-A. T. Stratton and F. E. Browder ABSTRACT: A system for reducing noise generated in an electrical transformer due to changing of size and shape of the ferromagnetic core when excited with alternating electric current. The noise reduction system comprises attaching flexible fibers to parts of the ferromagnetic core and parts of the housing or casing of the transformer. The flexible fibers absorb energy from the air column set up by the core when it changes size and shape and reduces the effectiveness of the air column in setting up objectional audible noise.

PAIENTEU HAY I 8 197:

v INVENTOR JAMES L. ROTRUCK NOISE REDUCTION SYSTEMS FOR ELECTRICAL TRANSFORMERS BACKGROUND OF THE INVENTION 1 Field of the Invention This invention relates to power transformers and more particularly to a noise reduction system comprising flexible fibers attached to parts of the core and easing of a power transformer.

2. Description of the Prior Art In the prior art transformers having a ferromagnetic core, when the core is excited with alternating electric current the core changes in size and shape because of the phenomenon known as magnetostriction. The core changes in size and shape at the rate of 120 cycles per second when the core is excited with 60-cycle alternating current. This continuous change in size and shape of the ferromagnetic core sets up an air column. This air column pounds against the sides of the casing of the transformer causing objectional audible noises to be generated. Audible noises are also generated by the individual laminations of the core when they change in size and shape. This invention reduces the effect of these audible noises which are set up by the changes in size and shape of the ferromagnetic core when excited by alternating electric current by coating at least parts of the core and the casing with flexible fibers. The fibers have only a portion of their length or one end attached to the core and the casing with the remainder of their length free to vibrate. These fibers tend to absorb energy which would nonnally go into an air column to generate objectional noise. It has been found that these fibers appreciably reduce the objectional audible noises created by the prior art transformers.

SUMMARY OF THE INVENTION The transformer provided by the present invention reduces the objection of the prior art devices by providing a coating of flexible fibers on the core and portions of the casing of the transformer. These fibers are of the order of one-eighth inch long and may be made of nylon, or any other suitable material. The fibers are attached to the core and the casing by means of a good adhesive such as varnish, epoxy or other material. The entire core and the entire casing may be covered with the fibers, or if desired only a portion of the core and a portion of the casing may be covered.

When the ferromagnetic core of the transformer is excited with 60-cycle alternating electric current, because of the phenomenon known as magnetostriction, the core will change in size and shape at the rate of 120 cycles per second. This continuous vibration of the core will set up an air column which will pound the adjacent parts of the transformer casing and generate objectional audible noise. It has been found that by coating the core parts and the casing parts with fibers as taught by this invention that the fibers tend to absorb the energy which would normally go into the air column and substantially reduce the audible noise generated because of the change in size and shape of the ferromagnetic core.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a partial perspective view, with parts broken away for purpose of clarity, illustrating the noise reduction system of this invention applied to a dry-type or air-cooled transformer; and

FIG. 2 is a schematic elevational view illustrating how the sound reduction system of this invention may be applied to a liquid filled transformer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the description which follows like reference characters refer to like elements on the various FIGS. of the drawings.

FIG. 1 is a partial perspective view, with parts broken away for the purpose of clarity, showing a dry-type or air-cooled transformer incorporating the present invention. The transformer 10 of FIG. 1 comprises a ferromagnetic core 12 madeup of stacked laminations of steeL'The core 12 shown in FIG. 1 is a three-phase core and has three legs 14, an upper yoke portion 16, and a lower yoke portion 18. Normally, windings 20 comprising concentric low voltage and high voltage windings will surround each of the leg portions 14 of the core 12. However, in FIG. 1 the winding 20 has been left off one of the legs 14 of the core 12 for the purpose of illustrating how fibers 22 are attached to the core 12. The transformer 10 comprising the ferromagnetic core 12 having windings 20 associated therewith is usually enclosed in a metallic casing 24. The casing 24 includes two sidewalls 26, two end walls 28, a bottom wall 30 and a top wall (broken away) similar to the bottom wall 30. This housing 24 completely encloses the transformer 10 comprising the core 12 and the associated windings 20.

The windings 20 of the transformer are usually excited with 60-cycle alternating current and a 60-cycle alternating current load is obtained from the secondary of the windings 20. When the windings 20 are excited with 60-cycle alternating current, due to the phenomenon known as magnetostriction, the ferromagnetic core 12 changes in size and shape at the rate of cycles per second. This continuous change in size and shape of the core 12 sets up an air column which extends to the walls of the casing 24. This air column pounds the walls of the casing at a rate of 120 cycles per second. This continuous pounding of the walls of the casing 24 by 24 air column causes the walls of the casing 24 to vibrate and generate objectionable audible noise. Audible noise is also generated by the continuous vibrations of the individual laminations 34 which are used to make up the ferromagnetic core 12. The noise due to the vibrations of the individual laminations 34 of the ferromagnetic core 12 and the sides of the metallic casing 24 is very objectional to the human ear. In the present invention this noise due to vibrations of the individual laminations 34 of the ferromagnetic core 12 and the sides of the metallic casing or housing 24 is materially reduced by attaching individual fibers 36 approximately one-eighth of an inch long to the exterior of the ferromagnetic core 12 and also to the inside of the walls of the metallic casing or housing 24. The fibers 36 may be of approximately one-eighth inch long and may be made of nylon, or like materials. The fibers are attached to the core I2 and to the walls of the casing 24 by means of varnish, epoxy, or some other good adhesive. The fibers 36 are attached to the metal parts at approximately one point on the fiber and the unattached portion of a fiber 36 is free to vibrate. The noise reduction system provided by this invention tends to absorb energy from the air column set up by the core when it changes in size and shape and reduces the effectiveness of this air column in generating audible noises objectional to the human ear.

In the embodiment of FIG. I the fibers 36 are attached to the entire exterior surface of the core 12 and to the entire inside surface of the walls of the casing 24. However, if desired only selected portions of the core 12 and selected portions of the walls of the casing 24 may have fibers 36 attached thereto.

FIG. 2 illustrates a liquid dielectric filled transformer incorporating this invention. In FIG. 2 the transformer comprises a ferromagnetic core 12 having windings 20 associated therewith. The core 12 and windings 20 are enclosed in a metallic casing 38. The oil column set up by the core 12 as it changes size and shape when excited by the windings 20 will pound the casing 38 and generate objectionable audible noise. This noise is reduced by attaching fibers 36 to the outside of the casing 38. The fibers 36 may be attached to the casing 38 in the same manner as they are attached to the core and casing in FIG. 1. If desired, fibers may also be attached to the core 12 in this embodiment to help further reduce the noise generated by the core.

Recorded below is a table of data taken first on a core with no fibers attached, and then on the same core having fibers at tached thereto, as taught by this invention.

TABLE I Core with no fibers Core with fibers attached Induction lines/cm. A-Scale-Db C-SealeDb A-Scale-Db C-Scale-Db The above tabulation of data shows relative sound level readings taken on a core with no fibers and readings taken on the same core with one-eighth inch long nylon fibers attached as taught by this invention. The readings were taken at six different inductions or flux levels. The readings were taken on a standard USASl, multiple scale sound level meter. Readings were taken on the A-Scale which records low pitch sounds heard by the human ear; and, also on the C-Scale which records higher pitch sounds heard by the human car. For each induction checked the readings on both the A-Scale and the C-Scale were substantially lower for the core having fibers attached than for the core with no fibers. This data indicates that the fibers reduced the noise level heard by the human ear.

The fibers 36 are attached to the core 12 and easing parts by first coating the part to which the fibers are to be attached with a good adhesive, such as varnish or epoxy. The part to which the fibers are to be attached is then charged negatively. The fibers are placed in a metal basket and the basket is changed positively. The basket is then directed toward the part to which the fibers are to be attached and shaken gently. Fibers will be projected into the liquid state varnish or epoxy coating on the part to which the fibers are to be attached and be attached thereto permanently when the varnish or epoxy adhesive dries.

From the foregoing description taken in connection with the drawings it is seen that his invention has provided a simple and effective noise reduction system for electrical transformers.

I claim:

1. A transformer comprising a ferromagnetic core which changes in size and shape when excited with electrical current, electrical windings to which electrical current is applied associated with said core for exciting said core, said core generating noise as it changes size and shape when excited with electrical current, means for reducing noise generated by said core when said electrical windings are excited with electrical current comprising fibers attached to at least parts of said ferromagnetic core.

2. The apparatus of claim 1 wherein said fibers are attached at substantially one point of said fibers to said ferromagnetic core with a substantial portion of their length not attached to said ferromagnetic core.

3. The apparatus of claim 1 wherein said fibers cover substantially the entire outer surface of said ferromagnetic core.

4. The apparatus of claim 1 including a casing enclosing the transformer wherein fibers are attached to at least parts of the inside of said metallic casing.

5. The apparatus of claim 1 including a casing for enclosing the transformer wherein fibers are attached to at least a portion of the outside of said casing.

6. The apparatus of claim 1 wherein said fibers are approximately one-eighth of an inch long and have one end attached to said core and the other end free to vibrate.

7. The apparatus of claim 1 wherein said fibers are made of nylon material.

8. The apparatus of claim 1 wherein said fibers are attached to said core by means of a coating of adhesive applied to said core, which adhesive attaches at least a portion of each of said fibers to said core. 

1. A transformer comprising a ferromagnetic core which changes in size and shape when excited with electrical current, electrical windings to which electrical current is applied associated with said core for exciting said core, said core generating noise as it changes size and shape when excited with electrical current, means for reducing noise generated by said core when said electrical windings are excited with electrical current comprising fibers attached to at least parts of said ferromagnetic core.
 2. The apparatus of claim 1 wherein said fibers are attached at substantially one point of said fibers to said ferromagnetic core with a substantial portion of their length not attached to said ferromagnetic core.
 3. The apparatus of claim 1 wherein said fibers cover substantially the entire outer surface of said ferromagnetic core.
 4. The apparatus of claim 1 including a casing enclosing the transformer wherein fibers are attached to at least parts of the inside of said metallic casing.
 5. The apparatus of claim 1 including a casing for enclosing the transformer wherein fibers are attached to at least a portion of the outside of said casing.
 6. The apparatus of claim 1 wherein said fibers are approximately one-eighth of an inch long and have one end attached to said core and the other end free to vibrate.
 7. The apparatus of Claim 1 wherein said fibers are made of nylon material.
 8. The apparatus of claim 1 wherein said fibers are attached to said core by means of a coating of adhesive applied to said core, which adhesive attaches at least a portion of each of said fibers to said core. 